The Study Of The Influence Of Bactericides On The Activity Of The Biofilm On SS316L And Its Corrosive Electrochemical Behaviour In Reclaimed Water

In this study,recirculating cooling water system in thermal power plant is selected as the research background.Stainless steel 316L(SS316L)is used as the study material.The reclaimed water and its three times concentrated water of secondary effluent from Beijing Gaobeidian recycling plant are used as the experimental medium and Sulfate Reducing Bacteria(SRB)are used as the experimental bacteria.And some bactericides in common use in the treatment process of circulating cooling water are used in this study:NaCIO,isothiazolinone,1227,XR-128 and TCCA.The best oxidizing bactericide NaClO and the best non-oxidizing bactericide isothiazolinone are selected during the study of the optimum concentration and the best action time of the five bactericides by means of microbiologic method.The enhancing efficiency of NaBr to NaClO is studied by measuring the concentration of residual chlorine in the water.And the sterilization mechanism of the compound bactericide XR-128 is studied.The influence of NaClO and XR-128 to SRB and its biofilm activity is studied by measuring the concentration of SRB and the amount of EPS(polysaccharide and protein)in water.The influence of NaClO and XR-128 to microbiological corrosion on the surface of stainless steel in reclaimed water and its three times concentrated water is studied by electrochemical method and X-ray photoelectron spectroscopy(XPS).In the meanwhile,the influence of the concentration ratio of reclaimed water to microbiological corrosion is also studied.The results are as follows:(1)By comparing NaClO,isothiazolinone,1227,XR-128 and TCCA,the sterilizing effect and duration of sterilizing of XR-128 are the best but within a short period(0?1d)the sterilizing effect of NaClO is the best.XR-128 is a typical cationic surface active agent of biquaternary ammonium salt.It can be absorbed preferentially on the surface of metal and improve the activation energy of electrochemical reaction.Also it can weaken the polysaccharide on the surface of SS316L,which relieves the corrosion of stainless steel.NaCIO used with NaBr can realize synergistic effect.Considering the pharmaceutical investment plus cost,4 mg·L-1 NaBr used with 20 mg·L-1 NaClO can have a better sterilizing effect and residual chlorine retention effect.(2)The growth phase of SRB concludes three stages(phase of adjustment hasn't shown up)in reclaimed water and concentrated 3 times water in which the concentration of SRB is 1×107 cell·ml-1.The first stage is the exponential phase of growth(0?1d),the second one is the stationary phase(1?7d)and the third one is the decline phase(after 7d).The increase of concentration ratio can accelerate metabolic of bacteria and enhance the biological activity of cells,thus increase the corrosion of stainless steel.Compared with NaCIO,after adding XR-128 the dehydrogenase activity of SRB cells is lower and duration of bactericidal effect is longer.(3)NaClO and XR-128 can have a strong inhibiting effect on EPS of SRB biofilm.NaClO has a better inhibiting effect on protein,while XR-128 has a better inhibiting effect on polysaccharide.In 3d,the inhibiting effect of NaCIO on protein is 46.4%,while the inhibiting effect of XR-128 on polysaccharide is 58.1%.(4)In the condition of no bactericides,the impedance arc diameter decreases and the corrosion rate increases with the passage of time in reclaimed water and three times concentrated water.NaClO can produce Cl-during the reaction,which may cause a damage to passive film and brings erosive deterioration.After adding XR-128,the impedance arc diameter increases,which shows that XR-128 can inhibit the activity of SRB and moderates corrosion.Besides,XR-128 won't spoil the passive film and it's safer.(5)After adding NaCIO,there is FeCl2 tested on the surface of SS316L,which means that NaClO has reduced and Cl-has produced.Cl-continually accumulates on the surface of stainless steel and has caused ion etching.After adding XR-128,Fe mainly combines with O and H,because XR-128 can form a protective film that will prevent corrosive ion such as S2-and Cl-and contribute to protecting the passive film on the surface of SS316L.After adding bactericides,the amount of S2-decreases obviously and there is no S2-tested in the three times reclaimed water.The result shows that XR-128 still has some bactericidal effect in 7d and it can work for a long time.